In recent years, there has been proposed a process for producing an addition polymer, which process comprises the step of polymerizing a monomer for addition polymerization such as an olefin using a catalyst, which catalyst is a combination of a transition metal compound such as a metallocene complex and a non-metallocene compound with a compound such as an aluminoxane. Such a catalyst is called a single site catalyst.
Examples thereof are a catalyst, which is a combination of bis (cyclopentadienyl) zirconium dichloride with methylaluminoxane (JP-A 58-19309); and a catalyst, which is a combination of bis(cyclopentadienyl)zirconium dimethyl with a boron compound such as tri(n-butyl)ammonium tetraxis(pentafluorophenyl)borate (JP-W 1-502036).
However, an addition polymer obtained by polymerization using these catalysts has problems that (1) its melt tension is not so satisfactorily high that a tubular film can not be molded speedily and steadily, and (2) its melt flow rate is not so satisfactorily high that it does not have good flowability.